Alcohol use disorder (AUD) is the third leading cause of preventable death in the United States. This disease has a negative impact on health, work, and relationships of the affected individuals. Research on the genetic and environmental determinants of the response to alcohol, and their relationship to the risk of developing AUD is critical to reducing the substantial societal burden of AUD. Genetic studies have shown association of AUD with gene variation in several loci. However, due to the heterogeneity in the AUD clinical phenotype and small effect sizes, there has been an increasing interest in examining the influence of gene variation on quantitative endophenotypes such as alcohol seeking, consumption, and brain circuit alterations. The present application focuses on the potential influence of gene variation in CHRNA5, the gene encoding the ?5 subunit of nicotinic acetylcholine receptors, on alcohol self-administration and brain circuit alterations. The rs16969968 missense single-nucleotide polymorphism (SNP) in CHRNA5 is associated with nicotine addiction and smoking-related consequences. However, despite the widely prevalent co-abuse of tobacco and alcohol, little work has been done to examine the effect of this SNP on alcohol use, dependence, or alcohol response. The goal of this proposal is to examine the influence of CHRNA5 variation on alcohol responses using an integrated translational pharmacogenetic approach that leverages the expertise of investigators at the NIAAA and NIDA intramural programs with the project PI to combine clinical research on human subjects and pre-clinical analyses in rodent models. A prospective study will compare alcohol self- administration behavior and neuroimaging responses in humans that are homozygous for the G-allele and those that are A-allele carriers of the CHRNA5 rs16969968 SNP. We will study the potential interaction of alcohol and nicotine by comparing smoking and non-smoking drinkers. To better understand the mechanistic link between CHRNA5 and alcohol response, we will conduct behavioral and functional studies in genetically modified animals expressing the ?5 gene variants or an ?5 null mutation. Similar to the human studies, we will study alcohol self-administration in nicotine-nave vs. nicotine-treated animals. Furthermore, we will study how CHRNA5 variation influences the effects of alcohol on the dopaminergic system by measuring ethanol-induced electrophysiological responses and dopamine release. Examination of the role of CHRNA5 variation in alcohol response will provide a greater understanding of the cholinergic mechanisms underlying the neurobiology of alcohol, with the goal of providing an expanded etiological spectrum for alcohol reward response phenotypes.